(1) Field of the Invention
The present invention relates to a VCA (Voltage Controlled Amplifier) circuit for adjusting an input signal and outputting an output signal, and more particularly to a VCA circuit for minimizing a DC offset when the VCA circuit has a maximum attenuation level.
(2) Description of the Prior Art
VCA circuits are used in communication devices, OA (Office Automation) devices, or the like, and include transistors forming differential amplifiers. Generally, a differential amplifier is composed of two transistors and functions as a current distribution cell. In actuality, the physical parameters of the two transistors do not coincide with each other. Hence, an offset voltage or an offset current is generated in the differential amplifier due to a mismatch of the physical parameters. The offset voltage or current causes an error in operation, particularly in a high-gain amplifier circuit in which the differential amplifier is placed at the first stage thereof. Hence, the offset voltage or current degrades the performance of the circuit.
The differential amplifier also has a DC offset appearing at its output terminal when an input voltage applied to an input terminal thereof is zero. For this reason, it is impossible to apply a feedback signal to the current distribution cell.